By E. Robert Bertolli, O.D.; and Dominic R. Pannone, O.D.
asers have become part of everyday life in the industrialized world since the ruby crystal laser was developed by Theodore H. Maiman at Hughes Aircraft and the gas laser by Arthur L. Schawlow and Charles H. Townes at Bell Laboratories, both in 1960. Prior directed-beam devices were only in the imagination of science fiction writers and in the pursuit of scientists. These days, most individuals have used laser-based devices routinely, if not consciously, including laser pointers in the academic setting; store product scanners; compact disc and DVD players; and other medical, industrial, and entertainment technology, with an evergrowing list of applications.
With lasers becoming more commonplace and more easily accessible, the danger of individuals or groups using them to inflict harm—ranging from distraction and camera flash–like afterimages to permanent damage to the field of vision—has risen. Injuries have been reported both to the cornea (the front of the eye) and to the retina (the back of the eye). For actual tissue damage to occur, attackers would have to modify a low-power laser (such as a green 632-nanometer wavelength laser, typically less than five milliwatts unmodified); otherwise, a more difficult to acquire industrial or military-style device would have to be employed. Making modifications to commercially available lasers or acquiring industrial or military lasers implies a motive considerably more sinister than a desire to commit pranks. Law enforcement agencies must be aware of the possibility of terrorists or other criminals using these devices illegally for their own gain.
What Is a Laser?
The term laser stands for light amplification by stimulated emission of radiation. Lasers are designed in various wavelengths and powers, and they are classified according to the type and the amount of damage they can cause to living tissue.
Modes of Operation: Laser modes of operation include continuous or pulsed waves. A continuous laser is constantly “on.” A laser in pulsed mode is activated either in short flashes or in one brief flash. Laser classifications group types by power, depending on wavelength. Relating the potential for damage to living tissue is simpler and more practical.
The following is a very simplified summary of the classifications:
- Class I lasers are not able to produce damage, either because of low power output or because they are enclosed, preventing direct access during operation. Examples include laser printers or DVD players.
- Class II lasers tend to afford less risk of damage from the eyes’ aversion reflex, but prolonged forced viewing of several minutes may cause eye damage. Many laser pointers fall into this category.
- Class IIIa lasers pose a hazard from direct view. This group includes some laser pointers and barcode scanners.
- Class IIIb lasers may pose a hazard from diffuse reflection of the beam as well as from direct viewing. Examples include entertainment laser displays (laser light shows) and the lasers used in some scientific instruments.
- Class IV lasers pose a threat to vision from direct, reflected, and diffuse reflection (that is, from dull surfaces), and the direct intra beam may also ignite materials and burn skin. This group includes surgical lasers and material-cutting lasers.1
Wavelengths and Ocular Consequences: Eye tissue damage takes place due to that particular tissue’s affinity to absorb a particular wavelength of light. The cornea absorbs ultraviolet and far infrared. (Refractive laser eye surgery, for example, employs an ultraviolet excimer laser to remove a controlled amount of corneal tissue, thus changing the way the eye bends light.) The internal crystalline lens of the eye absorbs ultraviolet and also microwave frequencies. The retina absorbs near infrared and visible laser wavelengths.
Invisible lasers (those whose wavelengths are in the ultraviolet or infrared range) are not perceived by the eye and give no visible clue of their presence until damage occurs. Carbon dioxide laser beams are one of the beams invisible to the human eye. This far infrared wavelength (10.6 microns) can shatter glass; crack windshields; opacify optics such as spectacle lenses, binocular lenses, and camera lenses; and ignite fuel at six kilometers (almost four miles). In a continuous wave, it will char flesh and destroy the cornea. In pulse mode, it will vaporize the front layers of the cornea.
The neodymium yttrium aluminum garnet (YAG) laser of 1,064 nanometers (near infrared) is also not visible, usually is in pulse mode, and is not filtered by aircraft windshields. This laser causes retinal tears as well as retinal and vitreal hemorrhages. Pulsed ruby lasers of 694 nanometers, green frequency doubled nd:YAG lasers (532 nm), and continuous wave argon blue-green lasers (514 nm) all cause retinal thermal burns, and pulsed mode will cause flash blindness, retinal burns, and vitreal and retinal hemes.2 Ultraviolet lasers, which as mentioned earlier have a beam invisible to the human eye, cause a photochemical reaction in living tissues, and pulsed mode causes corneal and skin burns.
Lasers as Weapons
In the military setting, extremely high-powered lasers have been developed for antimissile systems; more typically, military lasers are used for “blinding” optical components of enemy weapons systems or for ranging and target designation for guided munitions. However, combatant nations are forbidden by the Geneva Convention Protocol IV of October 13, 1995, from using lasers to blind enemy troops. Yet examples of such use exist, such as in the Iraq-Iran War, where range-finding lasers apparently featured or were perhaps modified to feature an antipersonnel mode. Iranian troops were reported to have ocular injuries consistent with such weapons.3
Information from a U.S. Federal Bureau of Investigation and Department of Homeland Security memo stated that al Qaeda had explored lasers as a weapon, including a possibility of lasing aircraft cockpits to interfere with pilots’ ability to operate their aircraft safely.4 The most vulnerable portion of a flight to such an attack is in landing.5 However, terrorism was reportedly not thought to be the cause of the numerous aircraft lasing incidents that have been reported. It must be noted that the Aum Shinrikyo cult in Japan, which executed the 1995 Tokyo subway sarin gas attack, was developing a fluoride laser for terrorism purposes.6
Lasing of aircraft, whether causing pilots to suffer actual ocular tissue damage or only temporary difficulties with vision, can result in crashes. In a lasing incident, pilots may experience any of the following: a dazzling effect, which temporarily disorients pilots (see figure 1); an afterimage lasting for several seconds, temporarily blinding them (similar to the afterimage experienced after being photographed with a flash); reddening, warming, or burning of the skin around the eyes; burning of the retina, causing permanent blind spots (in the medical profession referred to as scotoma); and bleeding into the vitreous as a result of a broken retinal blood vessel, which clouds vision. Any of these effects will cause pilots to experience visual impairment for a period of at least several seconds, if not minutes—placing the aircraft in grave danger.
|Figure 1. Laser dazzle of camera|
Aircraft have been lased many times both before and after the terrorist attacks of September 11, 2001. Some of these incidents occurred in a military setting: a Russian vessel suspected of lasing a U.S. military aircraft, resulting in pilot eye injuries; two U.S. helicopter pilots suffering eye injuries in Bosnia after lasers were aimed at them from the ground; and a suspected use by North Korea of ZM-87 neodymium military lasers on U.S. helicopters in the Korean demilitarized zone.7 Currently, the Chinese-made ZM-87 lasers are on the market for a relatively high price.8 The ZM-87 lasers have the capability of flash-blindness and even tissue damage at 10 kilometers (over 6 miles).9 Nonmilitary incidents include uses of lasers at landing aircraft in Salt Lake City, Utah; Teterboro, New Jersey; Colorado Springs, Colorado; and Sydney, Australia, as well as lasings of police helicopters.10
Lasing incidents are not limited to aircraft. A laser show accident at an outdoor rave in Moscow resulted in eye injuries to dozens of attendees.11 Other incidents have involved fire trucks, buses, and sporting events.12 Fortunately, slowing and stopping ground vehicles is one possible recourse to laser-induced visual impairment—unlike with aircraft.
Preventing Injury during a Lasing Incident
For any laser event, victims should close their eyes or move out of the line of sight to avoid further exposure. Closing one eye allows continued visual function while protecting the closed eye from exposure. If vision is compromised from an afterimage on the central retina, strategies such as eccentric, or indirect, viewing are helpful. By operating with peripheral (side) vision and using scanning movements of the eyes, no objects in the direction of travel are obscured by any blind spots (see figure 2). (Unfortunately, the sharpness of vision decreases exponentially as the distance between the center of the retina and the part of it used for vision increases. Instruments can be extremely difficult to read under such conditions.)
|Figure 2. By using eccentric or indirect viewing, vehicle operators can compensate for a laser-induced blind spot (scotoma), allowing them to see oncoming objects. Left to right: a normal field of vision; a simulated central scotoma obscuring objects in the direct line of sight; and simulated eccentric viewing moving the damaged center of vision away from oncoming objects, enabling them to be seen.|
Afterimages or blind spots occupy a fixed amount of space in a person’s field of vision. While a blind spot persists, objects located in that spot may be undetected. As an object comes nearer to the observer, however, the object projects an increasingly larger image on the observer’s retina, to the point that the image eventually exceeds the affected area and overlaps onto a functioning area. Retinal afterimages can last several seconds to several minutes before vision returns, whereas a retinal lesion—true damage to ocular tissues—may not ever return to normal function.
In a military setting, eye protection is available for lasers of particular wavelengths as anticipated by intelligence or as applied to training exercises. Protective lenses prevent potentially harmful wavelengths from reaching the ocular tissues.13 Industrial and medical laser operators use goggles to protect their eyes from the particular wavelength of the lasers they use. Regular spectacle lenses provide very little protection and may in fact focus the laser beam to cause more damage than no spectacles at all. Currently, however, the U.S. Department of Transportation does not recommend “new equipment for aircraft and aircrew.”14 In recent years, agilent lasers with changeable wavelengths have been developed, making protection more difficult. In an effort to adapt to the changing threat, a laser threat detection/warning system has been developed to warn pilots and determine the geographic origin of the beam.15
After an Incident
With any suspected lasing incident, the FAA requires reporting, and a medical eye evaluation should be considered for all potential victims.16 The exam should include visual acuity (in the form of an eye chart) and a grid pattern test (known as an Amsler grid) for scotoma as well as central visual distortion known as metamorphopsia. 17 Biomicroscopy should be performed to examine for corneal damage, and a dilated retinal evaluation should be performed for detecting possible hemorrhages and retinal lesions. If injury is apparent, the doctor will initiate the necessary therapy.
The introduction of laser use laws may discourage many pranksters, but unfortunately, there are those who will disregard any such laws and regulations. Technology is now providing cheaper, smaller, more powerful, more efficient lasers. In fact, the market is presently flooded with cheap class II and IIIa laser pointers, as well as industrial class IIIb and IV lasers and their components—which can be observed with just a quick search on eBay. Therefore, the potential for abuse remains. Whether motivated by malicious intent such as terrorism or carelessly implemented for stargazing or misguided amusement, recent lasing incidents should drive law enforcement agencies to take measures to guard against injury to their officers and the members of the communities they serve.
The authors have served as adjunct speakers at the Connecticut Police Academy on the medical aspects of horizontal gaze nystagmus (HGN), a type of impaired-driving test. ■
1University of Kentucky Environmental Health and Safety Division, “Fact Sheet: Laser Safety,” http://ehs.uky.edu/radiation/laser_fs.html (accessed January 7, 2009).
2U.S. Army Center for Health Promotion and Preventive Medicine (USACHPPM), Medical NBC Battlebook (Aberdeen Proving Ground, Maryland: USACHPPM, 2000), 6-10 to 6-15, http://www.bt.usf.edu/Reports/NBC%20battlebook.pdf (accessed January 12, 2009).
3“AFMIC [Armed Forces Medical Intelligence Center] Special Weekly Wire 32-90(C) (U),” released August 25, 1997, GulfLINK Document Index, Federation of American Scientists Intelligence Resource Program, http://www.fas.org/irp/gulf/cia/970825/970613_ww32_90c_D_txt_0001.html (accessed January 7, 2009).
4“Terrorists May Use Lasers to Blind Pilots, FBI Warns,” Los Angeles Times, December 10, 2004, http://articles.latimes.com/2004/dec/10/nation/na-lasers10 (accessed January 7, 2009).
5See Van B. Nakagawara et al., “The Effects of Laser Illumination on Operational and Visual Performance of Pilots Conducting Terminal Operations,” DOT/FAA/AM-03/12 (Washington, D.C.: Office of Aerospace Medicine, 2003).
6Kyle B. Olson, “Aum Shinrikyo: Once and Future Threat?” Emerging Infectious Diseases 5, no. 4 (1999): 513–516, http://www.cdc.gov/ncidod/EID/vol5no4/olson.htm (accessed January 7, 2009).
7“Russian Ship’s Laser Caused Eye Injury, Navy Officer Says,” Associated Press, February 12, 1999, Venik’s Aviation, http://www.aeronautics.ru/nws002/ap036.htm; “Lasers Burn U.S. Pilots’ Eyes,” ABC News, November 4, 1998, Federation of American Scientists Convention on Conventional Weapons (CCW) News, http://www.fas.org/nuke/control/ccw/news/bosnia981104_laser.html; “Report: N. Korea Fired Laser at U.S. Warplanes,” May 13, 2003, NewsMax.com, http://archive.newsmax.com/archives/articles/2003/5/13/74427.shtml (all accessed January 7, 2009).
8“Catalog: Missiles (Select) of China (2nd Artillery),” University of Wisconsin Colleges Department of Political Science, http://www.uwmc.uwc.edu/political_science/MIIIE/catalogmissilesc.htm (accessed January 13, 2009).
9Jane’s Chem-Bio Web, “Directed Energy Weapons and Sensors,” chap. 8 in China’s Aerospace and Defence Industry, December 1, 2000, Venik’s Aviation, http://www.aeronautics.ru/archive/research_literature/aviation_articles/Janes/topics/plasma_stealth/Directed%20Energy%20Weapons%20and%20Sensors.pdf (accessed January 7, 2009).
10“Laser Injures Delta Pilot’s Eye,” Washington Times, September 28, 2004, http://www.washingtontimes.com/national/20040928-111356-3924r.htm; Alan Levin, “N.J. Man Charged with Aiming Laser at Aircraft,” USA Today, January 4, 2005, http://www.usatoday.com/travel/news/2005-01-04-laser-aircraft_x.htm; “Green Lights at Airport,” Associated Press, December 29, 2004, http://www.kktv.com/home/headlines/1309846.html; Frank Walker, “City’s Worst Laser Attacks on Aircraft,” Sydney Morning Herald, March 30, 2008, http://www.smh.com.au/news/national/citys-worst-laser-attacks-on-aircraft/2008/03/29/1206207485440.html; “Laser Pointer Hits NYPD Helicopter,” Associated Press, August 1, 2006, http://www.boston.com/news/nation/articles/2006/08/01/laser_pointer_hits_nypd_helicopter/ (all accessed January 7, 2009).
11Chris Baldwin, “Ravers Lose Sight at Laser Show,” Reuters, July 14, 2008, http://www.reuters.com/article/healthNews/idUSL1452972520080714 (accessed January 7, 2009).
12See Appendix B in R. James Rockwell Jr., William J. Ertle, and C. Eugene Moss, “Safety Recommendations of Laser Pointers,” Rockwell Laser Industries, http://www-group.slac.stanford.edu/esh/hazardous_activities/laser/resources/Rockwell_Laser_pointer_safe.pdf (accessed January 7, 2009).
13USACHPPM, Medical NBC Battlebook, 6-20.
14“U.S. Secretary of Transportation Norman Y. Mineta Announces New Laser Warning and Reporting System for Pilots: Measures to Safeguard Pilots and Passengers, Support Timely Enforcement,” U.S. Department of Transportation press release, January 12, 2005, http://www.crcpd.org/Homeland_Security/LaserWarning.htm (accessed January 13, 2009).
15James Darcy, “New Navy Invention: Laser Detector Protects Pilots’ Eyes,” Navy Newstand, December 10, 2004, http://www.globalsecurity.org/military/library/news/2004/12/mil-041210-nns02.htm (accessed January 7, 2009).
16ATO-R System Operations Security, “Reporting of Laser Illumination of Aircraft,” Federal Aviation Administration Advisory Circular, U.S. DOT AC70-2, January 11, 2005, http://www.aopa.org/members/files/ac/ac70-2.pdf (accessed January 7, 2009); and USACHPPM, Medical NBC Battlebook, 6-3, 6-14, 6-15.
17USACHPPM, Medical NBC Battlebook, 6-14.